Neural mechanisms of foveal vision will be studied by means of single unit recording in the visual cortex of trained macaque monkeys. Eye position will be monitored in each animal by means of a surgically implanted coil in one or both eyes. Each animal's visual acuity will be optimized with correcting lenses. Additional psychophysical testing will include measurement of a) color recognition thresholds, b) eye dominance, and c) the presence or absence of an "oblique effect". Two particular aspects of foveal vision will be emphasized in these studies: 1) color vision and 2) fixation/localization. Electrophysiological recordings from single color cells will attempt to define the classes of color cells in three cortical areas (V1, V2, V4), and to examine the role of such cells in color perception by making each cell's responses relevant to the monkey's task. Fixation will be studied directly with the aid of the eye coil system. Possible neural mechanisms of localization will be examined in foveal V1 and foveal MT. In addition to retinotopic mapping in both areas, special attention will be paid in V1 to direction-selective cells of layer 4B and giant (Meynert) cells of layer 5/6, which have been shown to project to MT. Cells in MT will be examined with the eyes fixed at various orbital positions. Direction-selective cells in V1, V2, and MT will be studied while the monkey engages in slow pursuit tracking of moving fixation targets. Histological reconstructions of electrode tracks will be conducted using available computer techniques. Although disorders of color vision do not constitute a major clinical problem, the color perception system is a powerful model for feature-detection. Understanding the neural substrate for color vision would be a major step toward understanding perception in general. We orient ourselves in space in relation to the point of fixation. Accuracy and stability of fixation are essential for normal vision. Studies of the neural mechanisms which underlie fixation will provide information relevant to the management of eye movement disorders.